Presently, liquid crystal display panels and organic EL display panels are widely used in various forms, ranging from small and middle size display panels for use in cell phones, smartphones, and tablet PCs to large size display panels for use in television sets. Many of the liquid crystal display panels and organic EL display panels are active matrix type (or TFT type) display panels in which each pixel has a TFT (“pixel TFT”) and are characterized by high display quality, slim body, and light weight.
In recent years, the techniques for narrowing the frame region of a display panel have been advancing. The frame region refers to a region which surrounds the display region and which does not contribute to display. A monolithic display panel has been put into practice in which at least part of the driving circuit is provided on a TFT substrate of the display panel. The monolithic display panel has the advantages of narrow frame and low cost. For example, Patent Document 1 discloses a monolithic liquid crystal display panel.
Hereinafter, problems in conventional monolithic display panels will be described with an example of a liquid crystal display panel, although the problems are also common among other display panels which have a TFT substrate. For example, in organic EL display panels which have a TFT substrate, substantially all the circuit components are provided on the TFT substrate. However, to protect an organic EL element from the external environment, many of them have such a configuration that a protector substrate is provided so as to oppose the TFT substrate and that these substrates are adhered together by a seal portion.